Description:
We simulate the CCI1 and CCI2 detectors, using GEANT4, to study the figure of merit (FOM) for each detector. For both CCI1 and CCI2, we study how the FOM depends on strip pitch, z resolution, and lever-cut distance. For CCI2, we study how the FOM depends on the separation distance between the two silicon detectors, and the separation distance between the two germanium detectors. We also simulate future large-scale detector systems and calculate their FOM.

Description:
Simulations are performed using GEANT4 of a second-generation compact Compton imaging detector called CCI2 which uses silicon and germanium detector crystals. Realistic simulated detector geometry and realistic detector parameters are used. Results are obtained for the CCI2 detector for the intrinsic photopeak efficiency, imaging efficiency, and angular resolution, and simulated images are created for point sources with various energies and source angles.

Description:
We perform simulations of two types of large-scale Compton imaging detectors. The first type uses silicon and germanium detector crystals, and the second type uses silicon and CdZnTe (CZT) detector crystals. The simulations use realistic detector geometry and parameters. We analyze the performance of each type of detector, and we present results using receiver operating characteristics (ROC) curves.

Description:
ORNL's Technical Testing and Analysis Center (TTAC) acquired a High Purity Germanium Detector (HPGe) from ORTEC - a variant called an Interchangeable Detection Module (IDM). This detector has excellent energy resolution as well as high intrinsic efficiency. The purpose of this report is to detail the determination of the efficiency curve of the IDM, so future measurements can quantify the (otherwise unknown) activity of sources. Without such a curve, the activity cannot be directly reported by use of the IDM alone - a separate device such as an ion chamber would be required. This builds upon the capability of TTAC. The method for determining the energy-dependent intrinsic efficiency is laid-out in this report. It's noteworthy that this basic technique can be applied to any spectroscopic radiation detector, independent of the specific type (e.g. NaI, CzT, ClYC).

Description:
The IAEA has expressed a need for improved determination of gamma emitting nuclides in environmental samples collected during inspections of nuclear facilities and to use the MGA++ to determine U and Pu concentrations and isotopic compositions when those elements are present in relatively high concentrations. We are addressing the IAEA needs by evaluating the applicability of extended-range germanium detectors (ERG). In this paper we used 1g U isotopic standards and 100ug Pu liquid standards (1) to determine the performance of MGA++ on this special detector and (2) to estimate the amount of U and Pu necessary in the sample for determination of the isotopics via MGA++ within reasonable accuracy for a week of counting time using this ERG detector.

Description:
A technique has been developed at the Idaho National Engineering Laboratory to sum high resolution gamma-ray pulse spectra from systems with multiple Ge detectors. Lockheed Martin Idaho Technologies Company operates a multi-detector spectrometer configuration at the Stored Waste Examination Pilot Plant facility which is used to characterize the radio nuclide contents in waste drums destined for shipment to Waste Isolation Pilot Plant. This summing technique was developed to increase the sensitivity of the system, reduce the count times required to properly quantify the radionuclides and provide a more consistent methodology for combining data collected from multiple detectors. In spectrometer systems with multiple detectors looking at non homogenous waste forms it is often difficult to combine individual spectrum analysis results from each detector to obtain a meaningful result for the total waste container. This is particularly true when the counting statistics in each individual spectrum are poor. The spectrum summing technique adds the spectra collected by each detector into a single spectrum which has better counting statistics than each individual spectrum. A normal spectral analysis program can then be used to analyze the sum spectrum to obtain radio nuclide values which have smaller errors and do not have to be further manipulated to obtain results for the total waste container.

Description:
Even though technically innovative, a tunable crystal diffraction telescope for use in nuclear astrophysics has become feasible today. The focusing gamma-ray telescope the authors intended to propose for the space station consists of a tunable crystal diffraction lens, focusing gamma-rays onto a small array of Germanium detectors perched on an extendible boom. While the weight of such an instrument is less than 500 kg, it features an angular resolution of 15 inches, an energy resolution of 2 keV and a 3 {sigma} sensitivity of a few times 10{sup {minus}7} photons{center_dot}s{sup {minus}1}{center_dot}cm{sup {minus}2} (10{sup 6} sec observation) for any individual narrow line at energies between 200--1,300 keV. This experience would greatly profit from the continuous presence of man on the station. Besides of the infrastructure for maintenance and servicing of the various innovative techniques used for the first time in space, the available extra-vehicular robotics will facilitate deployment of the required boom structure.

Description:
The end of the Cold War has brought about tremendous changes in the nuclear complex of the Department of Energy. One of the many changes has been the shutdown or decommissioning of many facilities that performed nuclear work. One of the steps in the process of decommissioning a facility involves the decontamination or removal of drain lines or pipes that may have carried radioactive materials at one time. The removal of all these pipes and drain lines to a nuclear disposal facility could be quite costly. It was suggested by Pacific Northwest National Laboratory (PNNL) that a germanium spectrometer could be built that could fit through straight pipes with a diameter as small as 5.08 cm (2 inches) and pass through curved pipes with a diameter as small as 7.6 cm (3 inches) such as that of a 3-inch p-trap in a drain line. The germanium spectrometer could then be used to simultaneously determine all gamma-ray emitting radionuclides in or surrounding the pipe. By showing the absence of any gamma-ray emitting radionuclides, the pipes could then be reused in place or disposed of as non-radioactive material, thus saving significantly in disposal costs. A germanium spectrometer system has been designed by PNNL and fabricated by Princeton Gamma Tech (PGT) that consists of three segments, each 4.84 cm in diameter and about 10 cm in length. Flexible stainless steel bellows were used to connect the segments. Segment 1 is a small liquid nitrogen reservoir. The reservoir is filled with a sponge-like material which enables the detector to be used in any orientation. A Stirling cycle refrigerator is under development which can replace the liquid nitrogen reservoir to provide continuous cooling and operation.

Description:
In this paper we will present the results from an experiment studying the {sup 196}Pt(n,xn) reactions for n < 14 at moderate to high angular momentum using the combination of the LANSCE/WNR spallation neutron source and the multi-Ge detector spectrometer, GEANIE.

Description:
Construction and performance of a monolithic quad-pixel Ge detector for fluorescence x-ray absorption spectroscopy (XAS) at synchrotron radiation sources are described. The detector semiconductor element has an active surface area of 4.0 cm{sup 2} which is electrically separated into four 1.0 cm{sup 2} pixels, with little interfacial dead volume. Spatial response of the array shows that cross-talk between adjacent pixels is < 10% for 5.9 keV photons that fall within 0.5 mm of the pixel boundaries. The detector electronics system uses pre-amplifiers built at LBNL with commercial Tennelec Model TC 244 amplifiers. Using an {sup 55}Fe test source (MnK{sub {alpha}}, 5.9 keV), energy resolution of better than 200 eV is achieved with a 4 {mu}sec peaking time. At 0.5 {mu}sec peaking time, pulse pileup results in a 75% throughput efficiency for an incoming count rate of 100 kHz. Initial XAS fluoresncece measurements at the beamline 4 wiggler end stations at SSRL show that the detector system has several advantages over commercial x-ray spectrometers for low-concentration counting.

Description:
Germanium detector systems with both high spectral resolution and good imaging capabilities to the problems of environmental remediation. Over the last year, much progress has been made. We have (1) developed and built amorphous-contact germanium detectors of increasing sophistication, (2) built and tested an array of four position sensitive germanium detectors, (3) demonstrated spectroscopy and imaging uses with 235U, and Results from this research were presented at the EMSP's first workshop in Chicago in 1998, at the SPIE Session in July 1999, and at the IEEE Nuclear Science Symposium in November 1998 and 1999. AMORPHOUS CONTACTS The goal of the amorphous contact effort was to extend the single element (pixel) amorphous technology developed by Luke et al. (1994) to double-sided orthogonal strip detectors. Amorphous contact provides multiple advantages over the current lithium contact technology. We have fabricated the first orthogonal strip detector with dimensions appropriate for field use. The detector has an active volume of 50 mm x 50 mm x 10 mm and has 25 x 25 strips (see Figure 1). It is currently undergoing tests. The resolution is {approx}12 keV FWHM, which is dominated by electronic noise. The noise was high because of the large capacitance and the non-optimal electronics used with the test cryostat.

Description:
Drifting a thick lithium-drifted counter (silicon and germanium) is a time-consuming operation that frequently results in a poor device, owing to inadequate knowledge of progress of the drifting operation. The drifting apparatus described here automatically controls the temperature of the detector that is being drifted to maintain the leakage current at a preselected value. While drifting proceeds, a continuous measurement is made of the distance of the lithium-drifted region from the opposite face of the wafer. When the drifted region reaches 30 mil or less from the back of the wafer a meter indicates the thickness of the undrifted region and, when this thickness falls below a preselected value, the temperature of the detector is automatically reduced to room temperature. The need for constant supervision of the drifting operation is thereby eliminated, and reliance on theoretical drift-rate calculations to predict the drift-through time is avoided. The technique has been applied to the manufacture of lithium-drifted silicon detectors with excellent results. The application of the technique to lithium-drifted germanium {gamma} detectors is also discussed briefly.

Description:
Progress has been made at the Stanford Linear Accelerator Center (SLAC) toward deciphering the remaining 10-20% of ancient Greek text contained in the Archimedes palimpsest. The text is known to contain valuable works by the mathematician, including the ''Method of Mechanical Theorems, the Equilibrium of Planes, On Floating Bodies'', and several diagrams as well. The only surviving copy of the text was recycled into a prayer book in the Middle Ages. The ink used to write on the goat skin parchment is partly composed of iron, which is visible by x-ray radiation. To image the palimpsest pages, the parchment is framed and placed in a stage that moves according to the raster method. When an x-ray beam strikes the parchment, the iron in the ink is detected by a germanium detector. The resulting signal is converted to a gray-scale image on the imaging program, Rasplot. It is extremely important that each line of data is perfectly aligned with the line that came before it because the image is scanned in two directions. The objectives of this experiment were to determine the best parameters for producing well-aligned images and to reduce the scanning time. Imaging half a page of parchment during previous beam time for this project was achieved in thirty hours. Equations were produced to evaluate count time, shutter time, and the number of pixels in this experiment. On Beamline 6-2 at the Stanford Synchrotron Radiation Laboratory (SSRL), actual scanning time was reduced by one fourth. The remaining pages were successfully imaged and sent to ancient Greek experts for translation.

Description:
The encapsulation of high-purity germnium detectors is very desirable in order to increase their versatility and reliability. However, rapid and extensive degradation is seen for all detectors made from detector grade crystals which are encapsulated in a simple vacuum. Extensive studies have shown that the cause of this degradation is hydrogen adsorption on the detector surface. There it causes the formation of a strong p/sup +/ inversion layer which in turn shunts the detector junction. Reliable encapsulation is shown to be achievable by the use of hydrogen-free germanium crystals. (auth)

Description:
The motivation for this study was to measure and analyze the activity of six (6) niobium (Nb) foils (the x-rays from an internal transition in Nb-93m) and apply this information with previously obtained activation foil data. The niobium data was used to determine the epithermal to MeV range for the neutron spectrum and fluence. The foil activation data was re-evaluated in a spectrum analysis code (STAY`SL) to provide new estimates of the exposure at the Los Alamos Spallation Radiation Effect Facility (LASREF). The activity of the niobium foils was measured and analyzed at the University of Missouri-Columbia (UMC) under the direction of Professor William Miller. The spectrum analysis was performed at the University of Missouri-Rolla (UMR) by Professor Gary Mueller.

Description:
Over the past 30 years, Monte Carlo simulation of photons interacting with matter has gradually improved to the extent that it now appears suitable for calibrating germanium detectors for counting efficiency in gamma-ray spectral analysis. The process is particularly useful because it can be applied for a variety of source shapes and spatial relations between source and detector by simply redefining the geometry, whereas calibration with radioactive standards requires a separate set of measurements for each source shape and location relative to the detector. Simulation accuracy was evaluated for two large (126% and 110%) and one medium-sized (20%) detectors with radioactive point sources at distances of 10 m, 1.6 m, and 0.50 m and with aqueous solutions in a 0.5-L reentrant beaker and in jars of similar volume but various dimensions. The sensitivity in comparing measured and simulated results was limited by a combined uncertainty of about 3% in the radioactive standards and experimental conditions. Simulation was performed with the MCNP-4 code.

Description:
A previous experimental evaluation of nine commercial gamma-ray spectroscopy systems demonstrated significant benefits of digital signal processing for improvements in the performance of high-resolution gamma-ray spectroscopy systems. Spectacular improvements in the energy resolution and throughput of germanium detectors were demonstrated for the DSPEC. Recently, a new, improved version of DSPEC, the DSPEC Plus, was developed. Results of the performance of the DSPEC Plus are compared to those of the DSPEC.

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